The purposes of this project are to (1) examine the respective contributions of central motor programming and afferent information in the control of arm movements in normal, parkinsonian, and cerebellar diseased humans and (2) to study the psychomotor performance of patients with motor disorders due to central pathology. The first set of experiments uses the techniques of recording electromyographic activity and kinematics of limb position while subjects manually match a target display with either a skilled ballistic or slow velocity movement with a handle whose displacement controls a visual display. Movement amplitude, presence or absence of visual feedback of position, and disturbances of the subject's movements are independent variables. Preliminary observations indicate that large movements are performed relatively accurately independent of manipulation of the experimental variables but that accurate performance of small movements becomes increasingly dependent on visual information and the absence of limb disturbances during movement. The second set of studies examines a variety of psychomotor variables from patients with Parkinson's disease. Tests of movement speed, reaction time, and gait abilities have provided measures that correlated with clinically determined fluctuations in drug efficacy.